Process of electroplating bronze



Patented Aug. 21, 1934 UNITED STATES PATENT OFFICE 1,970,549 PROCESS orELECTROPLATING BRONZE tion of Ohio No Drawing. Application August 14,1933 Serial No. 685,146

27 Claims.

The invention relates to a new process for producing ele'ctrodepositedcoatings upon a base metal either polished or unpolished.

The application is a continuation in part of our application, Serial No.569,852, filed October 19, 1931, and some features of this invention aredisclosed but not claimed in our application, Serial No. 569,853, filedOctober 19, 1931.

The primary object of the invention is to obtain a process for producinga coating adapted for use as an intermediate between a relatively roughpolished or unpolished base metal and a highly lustrous finish metalsuch as chromium.

Another object is to obtain a process for electrodepositing a coatingcomposition at a rapid rate and at low cost while still obtainingdesirable properties of an undercoating.

A further object is to produce an electrodeposit which can be built upto a considerable thickness without blistering or becoming roughened.

Another object is to obtain a process which can be successfully carriedout under commercial operating conditions over a wide range ofconditions such as bath composition, temperature, current density, etc.

An important object of the invention is to produce a coating adapted tobe easily buffed to a high polish.

Another object is to obtain a metal or composition that may beelectrodeposited over itself in successive layers.

Another object is to obtain a coating that is not only highly resistantto corrosion in itself but has that property of being electrodepositedto or buffed to a dense surface that closes up porosity within theelectrodeposited coating.

One of the chief objects of the invention is to obtain a process forplating bronze which may be maintained in commercial operation for longperiods of time with a minimum amount of regulation.

Another object is to provide a means for accurately regulating thecomposition of a bronze plating bath and the operating conditionswhereby consistently good electrodeposits of bronze may be commerciallyobtained over long periods of time.

These and other minor objects are obtained by the novel processhereinafter more fully described.

Our improved process is designed to give an electrodeposited coating ofa mixture or alloy comprising the two metals copper and tin.

55 The process comprises the electrolyzing of a so- (Cl. 204-2) i lutioncontaining a soluble copper compound and a soluble tin compound whilemaintaining the alkalinity thereof between certain pH values andmaintaining a certain amount of free cyanide. The composition of thebath is varied widely under different conditions, depending upon therequirement of the particular work under treatment. -We have found itmost desirable to use for the soluble copper compound copper cyanidefrom 10 to 90 grams per liter and for the soluble tin compound an alkalistannate such as sodium stannate from 10 to 90 grams per liter. It is tobe understood however that under some conditipns it is possible to useother copper compounds such, for example, as other cyanide compoundscontaining copper. It is also permissible to use other soluble tincompounds such as other soluble metal stannates.

For continuous operation it is desirable to use anodes which will besufficiently corroded during the electrolysis to maintain in theelectrolyte the same proportions of tin and copper; preferably theanodes comprising both copper and tin. A suitable electrolyte may bemade up by mixing the following ingredients within the ranges given:

Copper cyanide Sodium stannate Sodium hydroxide. N a0 Sodium cyanide(free). Sodium cyanide (total) 10 to grams per liter. 10 to 90 grams perliter. 0 to 30 grains per liter.

0 to 60 grams per liter. 15 to 195 grams per liter.

Copper cyanide 40 Sodium stannate 20 grams per liter Sodium cyanide(total)--- 65 grams per liter Sodium hydroxide 7 grams per liter Theabove formula will produce a bath having a free cyanide content ofapproximately 20 grams per liter and a pH of 13.0. s

The bath gives good electrodeposits at current densities from 1 to 80amperes per square foot and it is possible to carry the current densitymuch higher but with increasingly lower efficiency. A density of 320amperes per square foot has 110 grams per liter been used but thisresults in an abnormally high evolution of hydrogen and requires somemeans for inhibiting the hydrogen at the cathode in order to obtaincommercial satisfaction.

The recommended temperature of operation of the bath is between 15 and70 0., preferably 60 C.

The anodes used are preferably of a mixture or alloy of copper and tinsuitably heat treated, but anodes of pure copper and tin may be used inlieu thereof. I

It is a noteworthy fact that the alloy anodes show a very uniformcorrosion and an entire absence of polarization in contradistinction tothe opposite properties in many other electroplating processes.

This bath when operated at our preferred temperature and current densitywill produce an electrodeposit having a tin content of 13 to 16 percent.We have discovered however that unless the free cyanide and pH arecontrolled or maintained, erratic results will be obtained.- In facteither or both might become so low that the bath would becomeinoperative due to anode polarization and the depletion of the bath aswell as changing the tin content of the deposit to a point where it willnot serve the purpose intended.

It is therefore an important feature of this invention to control thealkalinity and free cyanide content of the bath within such limits as tomaintain the bath in commercial operation.

For the best commercial values we find it desirable to maintain thealkalinity of the bath between pH 12.9 and 18.1. Under some conditions,however, satisfactory results may be obtained with an alkalinity withinthe range from pH 12.8 .to 13.5. We have also found it possible toobtain actual deposits when the alkalinity has been within the rangefrom pH 11.7 to 13.8.

We have found that for the best commercial results it is desirable tomaintain the free cyanide content of the bath within the range of 15grams per liter to 25 grams per liter, although satisfactory results areoften obtained within the range of 10 to 45 grams per liter.

We have also discovered that the following factors influence thecomposition of the electrodeposit:

Increasing the temperature and free cyanide content or lowering the pHincreases the percent of tin.

With the preferred free cyanide and pH the maximum tin content togetherwith the maximum bufling properties is obtained at approximately 30amperes per square foot current density.

As stated above, the preferred process gives a bronze electrodeposithaving 13 to 16% tin. If it is desired to obtain an electrodeposit withless tin, the preferred process should be modifled to raise one or moreof the factors, pH, free cyanide, and current density. For a depositwith a greater proportion of tin, the preferred process is modified bylowering one or more of the same factors.

The anode used is preferably an alloy of copper and tin in theapproximate proportions of the electrodeposit obtained by the process,although it may vary as much as 10% or more, and still be operableproviding the current density, temperature, pH and free cyanide areproperly adjusted. The anode is heat treated to obtain maximum softnessby casting in a metal mold, cooling in the mold, heating to 1000 F.

for fifteen minutes and quenching in water. Other heat treatments forobtaining the alloy in a soft condition may sometimes be substituted.

For maintaining the bath in condition for commercial operation it isdesirable to frequently check the amount of alkalinity and free cyanidein the solution and to add the necessary amount of alkali cyanide and/oralkali hydroxide to bring the pH value and the free cyanide value withinthe preferred limits heretofore set forth. The copper and tin contentsneed not ordinarily be changed provided the anodes are of theapproximate composition of the electrodeposit, but it falls within thepurview of our invention to regulate the amount of the tin compoundand/or copper compound by adding (or subtracting) the original reagentsor their equivalents as heretofore described.

Our process may be used for electroplating directly on iron and itsalloys including steel. It may also be used for plating on other metalswhether they be the base metal or only a coating over another basemetal. Examples of such metals are copper, nickel, tin, cobalt, silver,as well as combinations of these metals such as nickel and cobalt,copper and zinc, cadmium and silver and copper and nickel. The abovemetals can also be electrodeposited over the alloy formed by ourprocess.

Qne of the principal uses of our process is in obtaining a coating uponan unusually rough surface which can readily be buffed to obtain a highluster, thereby permitting an overcoating of a bright metal such aschromium.

The alloy resulting from our process has the following outstandingproperties:

(a) A high spreading property.

(b) Easy bufiing.

(c) A low loss of metal upon buifing.

(d) High corrosion resistance.

(e) An improved surface for superimposing another coating.

(1) Allows other metals to be electroplated thereon in a smooth lustrouscondition.

(9) Does not peel even in thick deposits.

(It) Can be superimposed over itself.

Our process has the following advantageous properties:

1. High rate of deposition.

2. A greatly improved ability to be electrodeposited to a greaterthickness without becoming blistered or rough.

3. Ease of control.

4. A greater ability to produce a suitable coating over wide ranges ofsolution composition.

5. A greater ability to produce a suitable coating over wide ranges ofcurrent density.

6. A greater ability to produce a suitable coating over a wide range oftemperature.

7. More deposit per unit of power input.

8. The ability to control the composition of the plated coating byvarying the following: Current density, temperature, and composition ofsolution. v v

The electroplated coating may advantageously be used as an undercoat inthe production of bright metal finishes. For example in chromium platingan automobile radiator shell in order to obtain both resistance tocorrosion and high luster, it is common practice in the prior art totake the steel shell as it comes from the dies and subject it to aseries of polishing operations to remove die marks, cuts, slight metaldistortions, pits and other surface defects in the metal as otherwisethese blemishes would show 150 in the final finish. With our process, weare enabled to eliminate the polishing of the base metal andelectrodeposit our metal or alloy directly on the unpolished metal. Weplate a sufliciently thick coating of alloy so that it can be buffedwithout cutting through and because of the high spreading property ofthe alloy, the surface defects are completely obliterated leaving ahighly buffed smooth surface for the final finish. Several types offinishes may then be superposed on the bronze. For example, brightchromium may be directly superposed or a nickel layer may be deposited,then bufied and finally covered with chromium.

While our process for electrodepositingbronze makes it possible in manyinstances to eliminate the polishing of the foundation metal, it issometimes desirable to mechanically eliminate some of the major surfacedefects even though the surface is not given a highly polished finish.We have found that if the work is mechanically polished with an abrasiveas coarse as to 120,'our bronze plating process with its subsequentbuffing will provide a highly lustrous smooth finish. It is of courseunderstood that our process can be used also with a polished foundationmetal wherever desired.

While our process is capable of considerable modification, it ispreferable to maintain the variable factors within such limits as toobtain a coating being within 3 to 35 percent tin, the balance beingcopper.

A desirable composition. for automobile radiator shells is:

Copper 1 Tin 1 15% What we claim as our invention is:

1. The process of electrodepositing a copper tin coating comprisingelectrolyzing a solution containing a soluble tin compound and a solublecopper compound-and maintaining the alkalinity of said solution withinthe range from pH 11.7 to 13.8.

2. The process of electrodepositing a copper tin coating comprisingelectrolyzing a solution containing a soluble tin compound and a solublecopper compound and maintaining free cyanide in an amount not to exceed60 grams per liter.

3. The process of electrodepositing a copper tin coating comprisingelectrolyzing a solution containing a soluble tin compound and a solublecopper compound, maintaining the alkalinity of said solution within therange from pH 11.7 to 13.8 and maintaining free cyanide in an amount notto exceed 60 grams per liter.

4. The process of electrodepositing a copper tin coating comprisingpassing a current from an anode comprising copper and tin to a cathodein an electrolyte containing a soluble copper compound and a soluble tincompound, maintaining the alkalinity of said solution within the rangefrom pH 11.7 to 13.8 and maintaining free cyanide in an amount not toexceed 60 grams per liter.

5. The process of electrodepositing a copper tin coating comprisingpassing a current at a current density of from 1 to 80 amperes persquare foot from an anode comprising copper and tin to a cathode in anelectrolyte containing a soluble copper compound and a soluble tincompound, maintaining the alkalinity of said solution within the rangefrom pH 11.7 to 13.8 and maintaining free cyanide in an amount not toexceed 60 grams per liter.

6. The process as set forth in claim 3 where the copper compound is acyanide of copper in an amount from 10 to grams per liter.

7. The process as set forth in claim 3 where the tin compound is analkali stannate in an amount from 10 to 90 grams per liter.

8. The process of electrodepositing a coppertin coating which compriseselectrolyzing a solution comprising a soluble tin compound and a solublecopper compound, maintaining the alkalinity of said solution within therange from pH 12.8 to 13.5 and maintaining free cyanide.

9. The process of electrodepositing a coppertin coating which compriseselectrolyzing a solution comprising a soluble tin compound and a solublecopper compound, maintaining the alkalinity of said solution within therange from pH 12.9 to 13.1 and maintaining free cyanide.

10. The process of electrodepositing a coppertin coating which compriseselectrolyzing a solution comprising a soluble tin compound and a solublecopper compound, maintaining the alkalinity of said solution within therange from pH 12.8 to 13.5 and maintaining free cyanide between 10 and45 grams per liter.

'11. The process of electrodepositing a coppertin coating whichcomprises electrolyzing a solution comprising a soluble tin compound anda soluble copper compound, maintaining the alkalinity of said solutionwithin the range from pH 12.9 to 13.1 and maintaining free cyanidebetween 15 and 25 grams per liter.

12. The process of producing a metal finish which consists inelectrodepositing on an unpolished surface of the base metal an alloy ofcopper and tin, bufling the surface of said alloy to obtain a highlypolished mirror finishj'and electrodepositing a bright metal thereover.

13. The process of producing a metal finish which compriseselectrodepositing on an unpolished surface of the base metal a thickcoating of a metal composition comprising from 3 to 35% tin and thebalance copper, bufling said metal to remove the surface imperfectionsin the original base metal and obtain a bright finish, andelectrodepositing a bright metal finish.

14. The process of electroplating which comprises the electrolysis of anelectrolyte comprising soluble stannate, soluble copper, excess cyanideand alkali at current densities from 10 to 320 amperes per square footwith anodes comprising copper and tin.

15. The process of electroplating which comprises the electrolysis of anelectrolyte comprising copper cyanide, soluble stannate, free cyanideand alkali at current densities from 10 to 320 amperes per square footwith anodes comprising copper and tin.

16. The process of electroplating which comprises the electrolysis of anelectrolyte comprising copper cyanide, alkali stannate, alkali cyanideand caustic alkali at current densities from 10 to 320 amperes persquare foot with anodes comprising copper and tin.

17. The process of electroplating which comprises the electrolysis of anelectrolyte comprising at current densities from 10 to 320 amperes perGrams per liter Copper cyanide 10 to 90 Sodium stannate 10 to 90 sodiumhydroxide Mo 30 Sodium cyanide (free) Oto 60 Sodium cyanide (total) 15to 195 20. An electrolyte for electrodepositing a copper-tin coatingcomprising:

Grams per liter Copper cyanide 40 Sodium stannate 20 Sodium cyanide(total) 65 Sodium hydroxide 7 21. An electrolyte for electrodepositing acopper-tin coating comprising a. soluble stannate, a soluble coppercompound, an alkali and free cyanide.

22. An electrolyte for electrodepositing a copper-tin coating comprisinga soluble stannate, a soluble copper compound and free cyanide.

23. An electrolyte for electrodepositing a cop- I per-tin coatingcomprising a soluble stannate and copper cyanide.

24. An electrolyte for electrodepositing a copper-tin coating comprisinga soluble stannate, copper cyanide and free cyanide.

25. An electrolyte for electrodepositing a copper-tin coating comprisinga soluble stannate, copper cyanide, free cyanide and alkali.

26. The process of electrodepositing a coppertin coating which compriseselectrolyzing a solution comprising a soluble tin compound and a solublecopper compound, maintaining the alkalinity of said solution within therange from pH 11.7 to 13.8 and using an anode comprising copper and tin.

27. The process of electrodepositing a coppertin coating which compriseselectrolyzing a solution comprising a soluble tin compound and a solublecopper compound, maintaining the alkalinity of said solution within therange from pH 11.7 to 13.8 and using a heat treated anode comprisingcopper and tin.

HARRISON M. BATTEN. CARL J. WELCOME.

